Communication Efficiency of Quantum Systems

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National Aeronautics and Space Administration, 1969 - Quantum communication - 22 pages
This report presents a method for evaluating the theoretical performance of quantum communication systems based on the communication efficiency parameter, β = P/NoR. For Gaussian systems, β represents the minimum average amount of energy required to decipher a bit of information, with zero error, in the presence of white noise of spectral density No. For certain quantum systems, the Gaussian result is directly applicable with No replaced by hv. In general, β is recognized to be the minimum number of average (photon) events required to decipher a bit of information with zero error. To make comparisons with Gaussian systems, the parameter K is introduced and hv/K becomes the effective Gaussian spectral density of the quantum system. Several systems are considered in addition to the capacity bound for the narrow-band quantum channel introduced by Gordon. Unlike the Gaussian channel, there is no lower bound on β as the bandwidth-to-data-rate ratio, α, is increased. Thus β can be continually decreased at the expense of average data rate. For large values of α, PPM direct detection asymptotically approaches the lower bound for β

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